What is a DC to DC charger and should my RV be equipped with one?
Before that question can be answered, you will need to understand what a DC to DC charger is and what functions it performs. Many of you reading this use an autoformer to assure the incoming shore power is at the proper voltage for your RV. As most of you know, low shore power voltage can damage the compressor in your air conditioning system and/or residential refrigerator, or cause a host of other problems. An autoformer adjusts, or what some say “conditions,” the voltage to the ideal level for your RV.A DC to DC charger functions much the same way as an autoformer by conditioning the 12 volts from your alternator to the ideal charging voltage for your house batteries.
What has recently changed that now requires a DC to DC charger on tow vehicles?
To meet mileage requirements, vehicle manufacturers began using “smart alternators” (aka variable voltage alternators) several years ago. In simplified terms, a smart alternator saves fuel by only supplying the immediate electrical needs for the vehicle. Reduced electrical load by the alternator equates to less mechanical load on the engine, which equals better fuel mileage. Unfortunately for RVers, a smart alternator is basically useless for charging auxiliary batteries in a travel trailer, fifth wheel or house portion of a motorhome. Even those with older “dumb” alternators can benefit from improved charge rates provided by a DC to DC charger.
Determining if your tow vehicle or motorhome has a smart alternator is rather easy. Click here to learn how.
Do I need one? Below are two scenarios to consider
1) If you hook up your RV, equipped with lead acid house batteries, to shore power every night, you probably won’t benefit from installing a DC to DC charger. Since the converter/charger in your RV keeps your house batteries charged while plugged in, your batteries will likely contain enough energy to supply your 12-volt needs while traveling between campsites. If you dry camp often or use a considerable amount of 12-volt power* while traveling between hookup campsites, you should definitely consider one. (*Running the slide outs in and out, residential refrigerator, 12-volt refrigerator, operating the RV furnace, using other appliances via an inverter, etc.)
Here’s why: A DC to DC charger installed on your RV acts like a 3-stage RV converter/charger powered by your alternator. It will condition or “step up” the voltage from the alternator to maximize battery charging, then step down and maintain the voltage as the house batteries reach full charge. This will charge your house batteries faster and more efficiently via the alternator when driving compared to not utilizing one.
May need to consider a charger
2) If you are considering installing lithium house batteries, especially in a motorhome, you will want to seriously consider a charger. Here’s why: Due to less internal resistance, lithium batteries can be charged and discharged much faster than conventional lead acid batteries.
A discharged lithium battery can demand more amperage than your alternator can readily supply. Overloading and damage to your alternator can occur when this happens. This is especially true when the house batteries are located in close proximity to the alternator, as you will likely find in a motorhome. This is due to less voltage drop over a shorter length of wire. Longer lengths of wire, like you would find between the alternator of a tow vehicle and the towable RV house batteries, typically provide enough resistance to protect the alternator.
This is another case where you will want to condition the 12 volts to an appropriate level. Just as a DC to DC charger can increase the charge rate to better charge your house batteries quicker, it can also limit the charge rate to protect an alternator when excessive power is demanded to charge lithium house batteries.
If you decide to install one, installation is relatively easy for do-it-yourselfers.
Hopefully, this short introduction to DC to DC chargers has helped you to understand what they are and how you might benefit from one.
They make a great Christmas gift for the RVer on your gift list!
Special thanks to REDARC for supplying a charger to the author for review and testing.